There are many uses for level sensing, particularly in the construction and power tool fields. For example, carpenter routinely uses a bubble level in rough and finish carpentry, and power tools such as drills frequently incorporate a bubble level to help the user maintain a true horizontal or vertical orientation of the tool.
Electric indicators have also been used, such as in the U.S. Pat. No. 4,189,726 to Rosa et al., which discloses an electric drill with an integral gravity-actuated electric switch including a spherical steel ball that travels in a circular path and bridges pairs of electrical terminals to complete an electrical circuit through an indicator lamp when the drill is oriented in true horizontal or vertical directions. And this approach may be extended, as disclosed in the U.S. Pat. No. 6,455,790 to Ogden for example, to create an angular orientation sensor with multiple sets of contacts distributed along a curved two-dimensional or three-dimensional path. However, what is frequently needed in the construction field is a sensor that indicates when a workpiece such as a framing board, metal conduit or construction guide is oriented at a user-specified angle with respect to true horizontal.